Electromagnet.



W. C. REED.

ELECTRGMAGNET.

APPLICATNN min MN. so, 1913.

1 ,209,646 A Patented D06. 19, l.

' the advantage that it is very economical as.

UNITED sTATEs PATENT oEEIFoE.

WALTER GQREED, or nALToN, MASSACHUSETTS, AsSIeNon To THE TELELECTBIC AcoMrAmr, 0E PITTSFIELD, MASSACHUSETTS, A 'CORPORATION oE1slAss".LoHu5A Specification of Letters Patent.

ELECTROMAGNET.

Patented Dee. 19, 1916.

Application led'January 30, 1913. Serial No. 745,095.

of Massachusetts, have invented new andl useful Improvements in Electromagnets, of which the following is a specification.

This invention is particularly intended t0 provide an electro-magnet which will beserviceable in connection with automatic piano-playing apparatus for operating a pedal of the piano. Such a magnet Should be capable of exerting a strong pull and of operating very quickly, and these character'- isticS-are found to a marked degree in the magnet hereinafter described, which also has regards the consumption oelectric current.

The features of construction and arrangement in which my inventionresides are hereinafter described in connection with the a'ccompanying drawing, in which- Figure 1 is a top plan view of my pedaloperating magnet as preferably constructed and Fig. 2 is a central longitudinal section through the same, showing certain associated parts in side elevation. x

The magnet shown in the drawing, which is of the solenoid type, comprises two tubular soft iron cores 2-2 surrounded by the wire coil 3 'of the magnet and separated within the coil by a space 4 which may be filled with non-magnetic material if desired but is in effect a gap. The coil is surrounded by a soft iron shell or jacket 5, and the spaces between. the cores 2 and the jacket 4 at the ends of the coil are bridged soft iron disks 6, thus forming a magnetic circuit around the coil 3 which is complete eX- cept at the gap 4, where a high reluctance exists.

posts 8 through which the circuit wires are connected to the ends of the coil, and preferably the cores 2 are lined with a very thin brass tube 9.

In the hollow interior of the magnet is located a soft iron plunger 10, which is adapted to slide longitudinally in the tube 9 and is -connected by suitable means to the part which is 4to be operated by the magnet. In the example represented, in which the magnet occupies a vertical position, a link 11 is pivoted at its lower end within a vertical slot in the upper end of the plunger and mechanism of the lin .its uppermost position.

The parts above described are se `cured to a suitable base 7 having' binding ing it to a pull wire 16 or the like. This wire 16 is intended to be connected totheydamper iano, and, by-.Xlocating said wire in a suita le one o the, 'oles 15 the extent of its movement maybe regulated as circumstances may require. An additional'capacity for adjustment of these parts is secured by providing the link 11 with a perforation at each end and also with an intermediate perforation located at different distances. from the end perforations, so that said link may bepivot'ed to the plunger atl either end and to the lever 12' at its opposite end or between its ends, as desired.

For arresting the upward movement of the plunger 10. and connected parts I prefer to employ a stop" consisting of a spring strip 17 secured to the lever 12 and having its freeend located in position to abut against the exterior of the magnet when the plunger is The yielding character vof the strip 17 preventsshock and noise in the operationof the magnet, and

strip is providedwith a felt tip 18.

The fixed soft iron parts included in the magnetic circuit are preferably given such dimensions that their cros`s-sectional area at any pointl in the circuit is at least equal to for the same purpose the free end of said v the cross-sectional area of the plunger 10,V

which has' a greater length than the gap 4 and a diameter Substantially equal to the internal diameter of the cores 2, so that when said plunger is in its uppermost or normal position, in which it is located mainly within the upper core 2, there is practically no reluctance between it and ,said core. lVhen inA this position the lower end of the plunger is located somewhat above the lower core'2 and preferably about midway ofthe gap 4, as shown in Fig. 2.

The result ofthe construction above described is that when the magnet is energized the magnetic stress is concentrated within a very small space,namely, the space between the lower end of the plunger 10 and the upper end of the lower corel 2, and the stress thus concentrated exerts on the plunger apowerful attracting effect which grows the plunger enters the plane of the upper end ol the lower or attracting core. From this point the plunger moves into saic core until a sullicient area of the plunger has been enveloped thereby to satisfy the magnetic flux through the iron circuit, which requires but a short movement of the plunger, and hence said )lunc'er 1s not onl sul) ected to a powerful pull butV also has a relatively small range el movement. These t'acts, in connection with the iact that the plunger is comparatively light as compared with the total wweight ot' the magnet, result in giving' the magnet the capacity to operate very rapidly with all the 'force required for actuating the damper mechanism of a piano. lvlagnets of similar construction may also be used with good results for operating the keys ol,g a piano, and in fact in various other situations where strength and rapidity of action are desirable, as will be evident.

The lower end olE the plunger l() is preferably concaved as shown at 19 in order to increase the concentration of the magnetic stress at this point, but this is not essential, nor is it essential that'the gap 4 occupy a position midway between the ends of the magnet.

Various other changes in the construction and arrangement of the parts may be made without departing from my invention.

I claim l. An electro-magnet comprising a cylindrical coil, a soft iron casing including a tubillar core and completely inclosing the coil externally and internally except for an annular gap Within the coil, the Width of the gap being inuch less than the length of said coil, a soft iron plunger arranged to slide longitudinally within the tubular core and substantially lling the latter transversely, said plunger having a greater length than the gap and being movable across the latter,

incendie means for connecting the plunger to the part to be operated thereby5 and a, spring for normally maintaining said plunger with its forward end located .opposite said gap.

2. An 'electro-magnet comprising a cylindrical coil, a soft iron casing including a tubular core and completely inclosing the coil externally and internally except for a gap within the coil, the width ot' the gap being much less than the length of said coil,7 a soft liron plunger arranged to slide long'itlulinally within the Atubular core and substantially llling' the latter transversely, said plunger being' movable across the gap and having a, greater length than the latter and a crosssectional areay not exceeding the cross-sectional area o1Ll the easing at any point in the magnetic circuit, means lor connecting the plunger to the part to be operated thereby. and a spring for normally maintainingr said plunger with its forward end located opposite said gap.

3. An electro-magnet oenlprising a cylindrical coil. a sott iron easing completely inclosing' the saine externally and internally except for a gap the Width of which is much less than the length o'i the coil. ay soft iron plunger movable across the gap in proximity to the easing, a pivotally-inounted arm and connections between the saine and the plunger, means for elevating said plunger, and a spring strip secured to said arm and constituting a stop located in position to maintain the forward end of the plunger opposite said gap.

n testimonyA whereof, il have hereunto subscribed my naine this 24th day of .la nary, 1913.

lvl/'ALTER C. REED. Witnesses z PHILIP W. Gonwn'r', @iconen l). Rens. 

